1. Field of the Invention
The present invention relates to a dual door type rotary nozzle system which is attached to the steel shell of a vessel for molten steel such as a ladle or tundish, whereby its slide plate brick is rotated so as to adjust the opening and closing or the degree of opening of a nozzle bore formed in a fixed bottom plate brick, and thereby to control the start, stop and rate of pouring of molten steel.
2. Description of the Prior Art
Rotary nozzle systems have been used widely with ladles for receiving the molten steel tapped from a converter to transport or pour the molten steel into molds, from tundishes for receiving the molten steel from a ladle to pour the molten steel into molds and the like.
Such a rotary nozzle system is generally mounted and supported on the base member fixed to the bottom shell of a molten steel vessel such as a ladle or tundish. The base member is fixedly fitted to the bottom shell of the vessel to enclose a top nozzle fitted in the vessel and having a nozzle bore, and a bottom plate brick is attached to the base member so as to align with the nozzle bore. A slide plate brick having a nozzle bore is pressed in surface-to-surface contact against the bottom plate brick by a support frame supported on the base member, and arranged along one side of the system is a drive unit for rotating the slide plate brick having a collector nozzle attached to its lower part within the support frame. In this way, the slide plate brick is rotated so as to adjust the degree of opening of the nozzle bore.
Included among the known rotary nozzles is a dual door type rotary nozzle in which an inner door including a bottom plate brick and an outer door including a slide plate brick are pivoted by hinges so as to open and close these bricks, and this type of nozzle has a number of features that the contacting or sliding surfaces of the top nozzle, the bottom plate brick and the slide plate brick can be exposed to permit the confirmation of any damages on the brick surfaces by the naked eye, so that there is no need to prepare any standby set for replacing or repairing the bricks, so that the operation is easy, and so on.
Generally, this dual door type rotary nozzle has its bottom plate brick in the inner door pivotably attached to a base member and the nozzle bore formed in the bottom plate brick is connected to a top nozzle projected from a molten steel vessel when the inner door is closed. Further, when the outer door is closed, a slide plate brick having one or more nozzle bores is held is close contact with the lower surface of the bottom plate brick by means of springs and the slide plate brick is rotated so as to adjust the degree of register between the nozzle bores (or the degree of opening). Also, it has recently been proposed to form two nozzle bores symmetrically in the bottom plate brick, and the bottom plate brick can be rotated so as to use the nozzle bores by selectively connecting them with the top nozzle and thereby increase the service life of the expensive bottom plate bricks. Typical details of such proposal being set forth in U.S. patent application Ser. No. 354,535 filed Mar. 4, 1982, now U.S. Pat. No. 4,498,611, the teachings of which are hereby incorporated by reference.
However, in the use of the dual door type rotary nozzle of the above type, the following problems have been encountered and their early solution has been sought.
(1) Due to the manual rotating operation of the gear case surrounding the bottom plate brick in the inner door, there have been disadvantages that its nozzle bore changing operation requires a great deal of effort and time.
(2) While the outer door including the slide plate brick is pivotably attached by a hinge to the base member fixedly attached to the bottom shell of the molten steel vessel so as to be opened and closed by means of the hinge, from the standpoint of safety control it is absolutely necessary that upon closing the outer door the bottom plate brick and the slide plate brick are held in close contact with each other so as to prevent the leakage of molten steel and the entry of air, and also the inner and outer doors are locked positively so as to prevent the doors from being opened during the pouring operation.
Thus, it has been the usual practice that when the doors are closed, they are threadedly locked by means of two upper and lower pins inserted through the base member and the outer door on the opposite side to the hinge of the outer door. With this type of locking mechanism employing pins, however, there is a disadvantage in that when the outer door is to be opened, it is difficult to remove the pins due to skewing caused between the pins and the engaging portions, and moreover the pins heated by the heat of the molten steel makes it impossible to touch the pins in sufficient time with the hands, hence making the operation difficult and requiring much time due to the small size of the pins. There are other disadvantages in that the locking mechanism for the pins is complicated and tends to be damaged easily.
(3) The dual door type rotary nozzle has its doors pivotably attached by the hinge to the base member attached to the bottom shell of the molten steel vessel, as mentioned previously, and the output from a reducer of a driving source, e.g., a motor, is transmitted through an intermediate gear to the gear of a rotor including the slide plate brick and provided in the outer door thereby rotating the rotor gear and hence the slide plate brick to adjust the opening of the nozzle.
In this case, due to the nonpivotability of the outer door owing to an interference between the gear of the rotor and the intermediate gear, it has been the usual practice with the opening and closing of the outer door that the intermediate gear is removed or the intermediate gear is shifted to disengage it with the rotor gear each time the outer door is to be opened or closed. However, there are a number of disadvantages that in the case of the former the weight of the intermediate gear is large and moreover the removing operation is difficult, thus requiring much time and labor for the operation, in that in the case of the latter the intermediate gear is exposed to a high temperature (about 300.degree. C.) due to the radiation heat of the molten steel and its smooth shifting is frequently prevented.
(4) Since the dual door type rotary nozzle is attached to the bottom shell of the molten steel vessel, during operation the rotary nozzle is heated to an elevated temperature of about 300.degree. C. by the radiation heat of the molten steel. This has the effect of heating and deteriorating the coiled springs adapted to hold the slide plate brick in close contact with the bottom plate brick through the rotor, and in order to prevent such a phenomenon air is supplied through the inlet hole formed in the outer wall of the outer door frame, circulated through the spring chamber and discharged to the outside through the other vent hole, thereby cooling the coiled springs.
However, while this cooling method is capable of satisfactorily cooling the coiled springs in the vicinity of the inlet hole through which air is supplied, due to the fact that during operation the coiled springs are compressed and the spring wire spacing is reduced (to 1 to 2 mm), the flow of the air is impeded with the result that the air heated during its passage through the spring chamber attains a considerably high temperature by the time it is discharged to the outside through the vent hole, and thus the coiled springs in the vicinity of the vent hole are practically not cooled entirely, thus causing variations in the cooling effect depending on the locations. As a result, there is a difference in performance between the coiled springs at places of good cooling effect and the coiled springs at places of bad cooling effect, and the pressing force on the rotor differs from one place to another, thus failing to hold the slide plate brick uniformly in close contact with the bottom plate brick and thereby causing leakage of the molten steel, the entry of air, or early wear and loss of the two bricks.
(5) The outer door for accommodating the slide plate brick and the rotor is pivotably attached to the base member by the hinge. In other words, a threaded pin consisting of a threaded portion and a supporting shaft portion is threadedly fitted in a threaded hole formed in each of the brackets on the base member, and a hole formed through each of the arms of the outer door is engaged with the supporting shaft portion directly or through a bearing thereby opening and closing the outer door.
With this type of hinge, however, due to the mechanism supporting the outer door by means of the end portion of the pin, the threaded pins are also rotated gradually during the opening and closing of the outer door, and moreover a change of shape is caused in the brackets of the base member if the weight of the door is large, thereby frequently displacing the door and preventing the slide plate brick from coming into proper register with the bottom plate brick. Also, once the door is displaced, it is impossible to bring the door back to the initial position through any fine adjustments of the threaded pins.
(6) The bottom plate brick cannot be made fast to the gear case by means of screws or the like in view of the gear case construction, and also the slide plate brick cannot be attached or made fast in view of the rotor construction. Therefor, there is the possibility of each of these plate bricks falling off the case or the rotor when the inner or outer door is opened, thus being dangerous and also tending to cause damage to these expensive plate bricks.
(7) The base member, to which the bottom plate brick is attached when the inner door is closed, is formed into a flat shape except that an annular stepped portion for receiving the bottom plate brick is formed along its inner peripheral edge, and an opening for receiving the top nozzle is formed at a position corresponding to the nozzle bore in the bottom plate brick. Therefore, a gap is formed between the lower surface of the base member and the upper surface of the bottom plate brick when the bottom plate brick is mounted in position.
Since the slide plate brick is pressed closely against the bottom plate brick by the springs as mentioned previously, excepting the nozzle bore portion backed up by the top nozzle, the slide plate brick cannot be pressed closely against the remaining part of the bottom plate brick due to the gap or the relief allowance, with the result that the interfacial pressure becomes unstable and there are instances where the bottom plate brick is deformed. As a result, the molten steel enters at the sliding surfaces of the bottom plate brick and the slide plate brick so that the bricks are damaged and their lives are reduced. Particularly in the case of the dual door type rotary nozzle system wherein the bottom plate brick is formed with two nozzle bores for the purpose of changing bores, such defects are manifested more markedly with the result that not only operation is impeded but also the frequency of repair and replacement of the expensive bottom and slide plate bricks is increased.
(8) Since the base member is welded to the bottom shell of the molten steel vessel, when it is desired to remove the entire system from the molten steel vessel for inspecting or replacing purposes, the entire system cannot be removed easily and the restoration operation takes time, thus giving rise to the danger of making it impossible to use the molten steel vessel over a long period of time and impeding operation.